Fruquintinib as a Maintenance Therapy Following First-line Treatment for Metastatic Colorectal Cancer

Inclusion Criteria: * 18-75 years old (including 18 and 75 years); * Eastern Cooperative Oncology Group-performance score (ECOG PS) 0 or 1; * Estimated survival ≥ 6 months; * Histologically and/or cytologically confirmed metastatic left-sided colon cancer with RAS mutation or right-sided colon cancer, having unresectable metastatic or recurrent foci; * Having received first-line systemic anti-tumor therapy for mCRC (chemotherapeutic drugs may include fluorouracil, oxaliplatin, irinotecan, such as XELOX, FOLFOX, FOLFIRI, and can combine or not combine with bevacizumab); achieving RECIST1.1-assessed SD (stable disease) or PR (partial response) or CR (complete response) after 18-24 weeks of first-line treatment. * UCG suggesting left ventricular ejection fraction ≥50%; * Having fully understood and voluntarily signed the informed consent. Exclusion Criteria: * Absolute neutrophil count (ANC) \<1.5×109/L, or platelet count \<80×109/L, or hemoglobin \< 9g/dL; it's not allowed to perform blood transfusion within 2 week before enrollment to meet the inclusion criteria; * Serum total bilirubin \> 1.5 × upper limit of normal (ULN); \> 2.5 × ULN for patients with hepatic metastases; * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \> 2.5 × ULN, or \> 5 × ULN for patients with hepatic metastases; * Serum creatinine \> 1.5 × upper limit of normal (ULN), or creatinine clearance \< 50mL / min (calculated using Cockcroft-Gault formula); * Partial prothrombin time (APTT) or prothrombin time (PT) \> 1.5 times ULN (based on the normal value in the clinical study center); * Clinically significant electrolyte abnormalities; * Urine protein 2+ or above, or 24-hour urinary protein quantity ≥ 1.0g / 24h; * Subjects with dysphagia or known drug absorption disorders; * Presence of brain metastasis or leptomeningeal metastasis; * The toxicity of previous anticancer treatment has not yet reduced to (NCI CTC AE) level 1, excluding alopecia and oxaliplatin-induced neurotoxicity ≤ 2); patients haven't not fully recovered from previous surgery or less than 4 weeks elapsed since previous anticancer treatment or surgery; * Patients have clinically detectable second primary malignant tumors at enrollment, or have other malignant tumors (except for well-treated basal cell carcinoma or cervical carcinoma in situ) in the past 5 years; * Patients have clinically uncontrolled active infections such as acute pneumonia, hepatitis B or hepatitis C activity (previous history of hepatitis B infection, whether or not under medication control, HBV DNA ≥ 104 copies or ≥ 2000 IU/ml); * Patients have hypertension that cannot be controlled by a single drug. That is, after single drug treatment, systolic blood pressure \>140 mmHg or diastolic blood pressure \>90 mmHg; * Patients currently have digestive tract diseases such as duodenal ulcer, ulcerative colitis, intestinal obstruction or other conditions that may cause gastrointestinal bleeding or perforation at the discretion of the investigator; or patients have undergone surgery for intestinal perforation and intestinal fistula but was uncured. * Patients have a history of arterial thrombosis or deep vein thrombosis within 6 months prior to enrollment, or patients have bleeding tendency or bleeding history within the 2 months before enrollment, regardless of severity; * Patients have a stroke or transient ischemic attack within 12 months prior to enrollment; * Skin wounds, surgical sites, trauma site, severe mucosal ulcers or fractures haven't completely healed yet. * Patients have acute myocardial infarction, severe/unstable angina, coronary artery bypass grafting or NYHA Class II/more severe cardiac insufficiency within 6 months prior to enrollment; * Pregnant or lactating women; or women with potentiality of childbearing have a positive pregnancy test result before the first dose; * Patients have any clinical or laboratory abnormalities or compliance problems so that the investigator believes that they are not suitable to participate in this clinical study; * Patients have serious psychological or mental abnormalities;